Generally, for example, referring to JP-2003-336989A, an inner-fin tube has a tube member and an inner fin member. The tube member is constructed of a band-shaped plate material by bending, to have a flat cross section. The tube member includes a bend portion and a swaged portion which are respectively arranged at two ends of the flat cross section. The inner fin member is constructed of a band-shaped plate material and arranged in the tube member. One end of the inner fin member contacts an inner wall of the bend portion of the tube member, and the other end of the inner fin member is fixed to the swaged portion of the tube member by swaging.
Therefore, a position deviation, a departure and the like of the inner fin member from the tube member are restricted. In this case, while the tube member and the inner fin member are continuously manufactured by a roller forming device, the inner fin member is continuously inserted into the tube member.
However, referring to JP-2003-336989A where the inner fin member is continuously inserted into the tube member via the roller forming device, the tube member and the inner fin member are formed in parallel and the inner fin member is bent toward a plate thickness direction of the band-shaped plate material to be merged into (inserted into) the tube member. The tube member is provided with an opening portion (where swaged portion will be provided) at a major-axis-direction end of the flat cross section of the tube member. After the inner fin member is inserted into the tube member, the side of the opening portion is swaged. Therefore, it is necessary for the inner fin member to be bent from the side of the major-axis-direction end of the flat cross section of the tube member in a width direction of the band-shaped plate material of the inner fin member, to be merged into the tube member through the opening portion.
However, generally, the band-shaped plate material cannot be bent in the width direction thereof, so that it is difficult for the continuous forming disclosed by JP-2003-336989A to be realized.